Rotary type air compressor



Sept. 26, 1950 D. F. MCGILL 2,523,317

ROTARY TYPE AIR COMPRESSOR Filed oct. so, 1943 2 sheets-sheet 1 Spt. 26, 1950 D. F. MoGlLL 2,523,317

ROTARXr TYPE AIR COMPRESSOR Filed Oct. so, 194:5 2 sheets-sheet 2 F fg. 5 25 Z! j I4 .f2 7l 64 l! I0 ,c 519 l@ 66 65 l I 9, f 57 J lll E HH f5 l Z Z7 36 Z9 ZZ I5 Patented Sept. 26, 1950 UNITED STATES PATENT OFFICE 2,523,317 ROTARY TYPE AIR COMPRESSOR Daniel F. McGill, Portland, oreg. Application October 30, 1943, Serial No. 508,369 13c1aims. (C1. 23o-152) This invention relates to new and useful improvements in rotary type air compressors.

It is the primary object o'f the invention to provide an air compressor having means for creating an expansion of air in the fluid chambers f the device for cooling the device. i

It is a further object of the invention to provide in an air compressor means for introducing air under pressure into the fluid chambers during travel thereof between suction and discharge sides of the pump in an amount suflicient to equalize the pressure between said fluid chambers and the compressed air tank.

It is a further object of the invention to provide in an air compressor means for circulating water for sealing purposes through the compressor under equal or greater pressure than the air pressure created by operation of the device.

It is a further object of the invention to provide an air compressor capable of producing cool, dry air.

It is a further object of the invention to provide in a rotary type air compressor means for withdrawing the rotor vanes from operative position during periods of inoperation of the compressor so as to unload the prime mover at time of startlng.

It is a further object of the invention to provide an air compressor of the rotary type in which the rotor vanes may be moved to inoperative position during rotation of the rotor to avoid the necessity of stopping and starting the motor between periods of operation.

The invention comprises a rotor mounted within an` elliptical chamber wherein the wall of the chamber between the intake and discharge ports is concentric with the rotor. Rotor vanes are arranged at intervals around the rotor, which, together with the rotor and chamber wall, define a plurality of uid chambers arranged for travel from the suction to the discharge sides of the pump. The vanes are so mounted in the rotor that each vane may move in and out of the rotor independently of the other vanes. The vanes are inclined forwardly in relation to the direction of rotation and are moved into engagement with the wall of the chamber by the pressure of lubricating and sealing liquid admitted to passages at the inner ends ofthe rotor vanes.

The sealing liquid may beled from the delivery side of the pump, or from a tank in which said liquid is subjected to the pressure developed by the pump, into passages at the inner ends of the rotor vanes to force them outwardly. In the preferred embodiment of the invention such liquid `2 is circulated through the compressor and back to' the tank by means of a centrifugal type pump attached to the rotor. By means of a pressure regulating valve'in the return pipe line the sealing and lubricating fluid may be utilized at a slightly higher pressure than that present in the aforementioned tank.

Another feature of the invention resides in the provision of an apparatus for introducing comv pressed air into the fluid chambers in the compressor during their travel between suction and discharge sides of the pump. As the compressed air passes into saidchambers it is expanded therewithin and is cooled by reason of its release from pressure, and in so doing absorbs the heat created by friction of the moving parts of the pump.

These and other desired objects and advantages 4 of the invention are obtained through the novel arrangement, the unique construction, and the improved combination of the various parts hereinafter described in conjunction with the accompanying drawings, it being understood that vari-l ous changes in form, proportion, size and details of construction within the scope of the claims may 'be resorted to without departing from the spiritl or sacrificing any of the advantages of the invention.

In the drawings: Figure 1 is a longitudinal sec- `tional view of an air compressor embodying the invention; Figure 2 is a transverse section of the` air compressor, taken on the line 2 2 of Figure l 'Y and including a diagrammatic sectional viewzof the tank and its related piping; Figure 3 is a longitudinal sectional view taken on the line 3 3 v'of Figure 1; Figure 4 is a diagrammatic drawing showing the development of the interior of the casing of the structure shown in Figures 1 and 2;

and Figure 5 is a side elevation of an apparatus illustrating the principle of operation of the invention. l p

In the illustrated embodiment of the invention the rotor I is mounted within a casing I I having heads I2 and I3, respectively, dening a pump coincident with the center of the rotorY I0. The opposite Wall of the chamber is described as a circular arc C-D subtending an angle'Y about a center S, which is spaced from the center R along the vertical axis of the chamber I4 by an suction and discharge sides of the pump. At the ends of the `ellipse formed by the arcs A-B and C-D the walls of the chamber may be described by rotating lines M-N through the angles O about centers T. The aros M-N and E-F intersect the arcs A-B and C-D tangentially with no sudden changes in direction, soA that rapid changes in rate of movement of the rotorivanes are avoided. Between the points M-M on the arc A-B, the wall of the chamber I4 is coaxial with the rotor lil. The points M, M dene'the termini of oppositely disposed inlet and discharge ports I- and If, respectively, and hence the iuid;v

chambers between adjacent rotor Yvanesdo not vary in size during their travel between suction and-discharge sides oi the pump.

In the device illustrated in the drawings, angles Y and Z are equal and the radius K ofthe arc A-B is equal to the radius K? of the arc C-D. It will be appreciated, however, that either of the angles Z or Y may be lengthened or shortened relative to the other according to the use to be made of the device, and that the radii of the respective aros will be lengthened and shortened proportionately.

YThe inlet port opening I5 extends, in the direction .of rotation, from the point E to point M, andY the discharge port opening lextends from point M topoint F. At the points E and F the vanes do .not project from the rotor. By extending the discharge port opening to the point F' fluidcannot be trapped ahead of each vanewhich, if no slippage or leakage were present, would operate tostopvthe pump.

The rotor Ill is provided with slots l'l extending in a direction inclined forwardly from the radius laof the-rotor, the slots being inclined forwardly in relationto therdirection of rotation. The slots I1 extend through the rotor from one side to the other and terminate at their inner ends. in passagesA I9 which communicate with the discharge or, a centrifugal -pump hereinafter more. specilically described. The slots Il form bearings in which vanes 2| are slidably mounted.. The outer endsof the vanes are ,beveled to conform asnearly as possible with the general contour of the inner wall of the casing ll. fact that throughout the Varo A-B the casing wall'visrcoaxial with the rotor IEB, there is no relative `movement between the vanes and the rotor By. reason of the.

tion counter tothe direction of rotation. Pressure onthe end of the vane tends to vmove thedischarge ports, and insures the presence of at least one vane in the sealing area Ee-F between suction and discharge sides of the pump.

A ,pipe line 3l leads from the discharge port i6 to a pipe connection 38 in the bottom of a tank 39 which may preferably be positioned at an elevation above the pump. Mounted within the tank 38 so as to form therewith an inclosure for the end of the pipe line 31 is a bale 4| having perforations 142 lproviding communication with the interior of the tank. It isv intended that the tank 39 shall contain an amount of water sufficient to submerge both the baffle 4i and a screen i3 mounted in the lower portion of the tank above the bafe. The baiile 4| serves to diffuse the air Each headis provided with a stufng box 2t having the usual packing members 25.

vThe headlSY is provided with an annular recess 25K and mounted :within this recess is a centrifugal pumpV element 2l. The centrifugal pump may comprise a circular disc 28 secured to the rotor H31. by. means ofv screws 29. An axial ange 3l supports. the disc 23 inspaced apart relation to the side wall of the rotor to'cause the disc 28 to overlie theV plate 32 forming the closure member for the adjacent end of the chamber i4.

The circular disc 28 is interruptedl adjacent the. shaft 22 .to providean intake or eye 33 from which fluid is suppliedto passages 3@ extending radially through the dis-c 28. The passages Sil discharge into the. volute area 35 from whence liquid flows through a passage between the plate 32.-,and. the circular disc 28 to an annular chamber 36 having communication with each of the passages i9 atthe inner ends of the slots El.

A pipeline 46. leads from a submerged portion ofV the, tankr 39,-to1 athreaded connection ll'l in the head i3 by means of which water is supplied to-an annular chamber 48 in the head i3 communicatingwiththe intake 33 'of the centrifugal pump 21.

55purnp21 The lwater circulated through the rotor carries therewith any dirt which may collect in the several passages associated with the centrifugal pump and rotor, and pipe line 4S may preferably be connected into thetank 39 at a point below the water level. e

It will be appreciated that the water in the lower portion of tank 38 is under the pressureY created by compression of the air in the tank. Operation of the centrifugal pump tends to eirculate the water from the tank through the passages laatY the inner ends of the -slots l1, along the side walls between the rotor and housing, and into' the annular chamber 5l in the head l2 on the opposite side of the rotor. From thence the lwater is" returned byv pipeline 139 tothe tank 39.

A' pressure regulating valve 59 in the pipe line A9- may be so adjusted that the water in the passagesv isis at a slightly higher pressure than the f water in the tank 39. For example, assuming that the water in the tank 39 is under a working the water entering the suction of the centrifugalpump is under pressure of one hundred pounds. The valve 59 may be adjusted to require a pressure of five pounds to operate the valve, thus .insuring a water pressure in the passages I 9 somewhat greater than the air pressure. lBy circulating the water through andV around the rotor structure in the compressor, leakage of air from the compressor is precluded, regardless of the pressure developed.

' The anglev of inclination of the vanes 2I is such that the inertia of each vane tends to hold the vane-within the body of the rotor II), and to require the application of some external force t move the vanes into engagement with the casing wall. This force is supplied through operation of the centrifugal pump 21, which coacts with the pressure regulating valve 59 to build up suiiicient pressure in the passages I9 to move the vanes outwardly of the slots I1 and into engagement with the casing wall. A pipe line 64 extends between the return line 49 and the intake pipe 65, by means of which the water may be withdrawn from the passages I9 to permit the vanes 2I to remain wholly within the slots I1. With the vanes in such inoperative position, continuous operation of the rotor may be permitted without delivery of air to the tank 39 and without fric` tion of vanes 2| on the casing wall. Avalve 61 is provided to close the pipe line 64' during operation of the compressor. During periods of inoperation of the compressor, a check valve 66 prevents escape of 'air from the tank 39- by way of pipeline 31; a valve 68 is provided for closing the pipe line 46 to facilitate withdrawal of the water from passages I9 and so permit the vanes 2| to move to inoperative position; a valve 69 is provided for closing the pipe line 56; a valve 10 is provided for .closing the pipe line 49; and valve 1I is operable to close the intake pipe 65. These valves may be interconnected for simultaneous operation by a master valve control mechanism (not shown) whenever the pressure in the tank is of a predetermined value. This arrangement of elements obviates the necessity of stopping the motor between periods of operation of the compressor.

A novel feature of the invention resides in thek provision of' means for admitting compressed air from the tank 39 into the chambers between adjacent rotor vanes 2I during the travel of such chambers from the suction to the discharge sides of the pump. It will be remembered that between the points M, M the capacity .of these chambers is constant. A header 52 is arranged adjacent the casing II, the header having communication with the chamber I4 by way of a plurality of nozzles 53a-b-c which are threaded into tapped orices in the casing II at points spaced apart by a distance greater than the distance between adjacent rotor. vanes 2I. While the drawings illustrate the nozzles 53a--b-c as being threaded into the casing II, it will be appreciated that the header 52 may be positioned adjacent the head i2 and that the nozzles 53 may be threaded into tapped orifices in the head. It is important, of course, that the orifices 54 be so positioned in either the casing II or'the head I2 as to permit the lnozzles 53 to discharge into successive fluid chambers between the rotor vanes 2I. Each of the nozzles 53 is equipped with a valve 55 for regulating the ow from the header 52 through the nozzles 53. The header `52 is conv nected with the tank 39 vby means of a pipe line 5BV 6". throug'hwhich air'from the tank V`39 is supplied to the vheader 52. Y-

In operation, air is admitted to the device by way of intake port I5 and is conveyed by way of chambers 51 between adjacent rotor vanes 2lr to the discharge port I6 from whence it is conducted by way of pipe line 31 to'the tank 39. vFor purposes of illustration, assuming that each chamber will contain one cubic foot of air at normal atmospheric pressure, in the structure as heretofore described 'the device will deliver one to ll the tank to a level above 'the screen 43 so v that thev stream ofv air entering the tank through the baiile 4I and screen 43 is cleansed by the intimate association of the air and water as the air passes through the water in the form of small bubbles. From the tank 39 the air is supplied by way of supply line 45 to a placeof use.

Air is also supplied from the tank 39 by way of pipe line 56 to the header 52 and from thence by way of nozzles 53a--h-c to the chambers 51. The rst nozzle 53a is so positioned as to introduce air under pressure from the header 52 into the chamber 51a whichl has just been closed by the rotor vane Zia. The valve 55a in the nozzle 53a is so adjusted that a predetermined volume of air at the pressure existing in the tank 39 will flow through the nozzle inthe period of time required for the passage of adjacent rotor vanes 2I past the nozzle orice lia. rotor vane has passed over the orice 54a of nozzle 53a, the leading rotor vane will have passed Y over the nozzle orifice of nozzle 53h, so that air is discharged into the chamber therethrough. The valve 55h in nozzle 53h is so adjusted as to admit into the chamber a predetermined volume of air at the pressure in the tank 39 within the period of time that the nozzle 53h is in communication with the chamber. After the trailing rotor vane ZI has passed over the orice of nozzle 53h the leading rotorvane uncovers the orifice of nozzle 53C, whereupon air is introduced rinto the chamber therethrough. The valve 55e in nozzle 53e is so adjusted as to introduce into the cham-y ber a predeterminedv volume of air at the pressure in the tank 39 within the period of time that the chamber is in communication with the nozzle 53C'.

For purposes ofclarifying the method of opera- Y" With a given opening through pipe line 63 la certain length of time is required for equalization of pressure between the two tanks. As the air passes into the smaller tank 62 it will be cooled by reason of its release from pressure. The smaller tank 62 is representative of the fluid chamber 51 in anair compressor embodying the instant invention, and the time required for the travel of the chamber 51 from thel suction' to the discharge sides of lthe pump represents the time required to equalize the pressure be- After the trailing twe'nzsthetank 39 and", the' chamber; initially`-` each of the uid chambers 51 islled with air at atmospheric'pressure and, assuming that the air Yinthe tank*` 39 is underr one hundred' pounds pressure, air in' an amount equal to approximately six cubic feet of free air is Vexpandedinto each of '.the chambers 51 and added to'the one cubic foot of freeV air contained thereWithin to equalize pressures between thev chambers andl the tank during Vthe travel of each chamber betWeensuction and discharge sides ofthe pump.

In a structure for handling large volumes of air itmay be ldesiredl to introduce air into each fluidlchamber through a plurality of nozzles. For example, in an air compressor comprising a rotor l0 of considerable width; any desired number of nozzles 53 Vmay be aligned transversely of theVV casing for introducing air into each successive fluid chamber., On the other hand, instead of employing nozzles spaced in the direction of travel of the fluid chamber, as herein illustrated and described, the desired cooling effect may be accomplished by the use of a single nozzle for ejecting air intoeach chamber passing the nozzle orifice. It should be understood, therefore, that the description of a particular 'arrangement of such nozzles isl not to be considered in a limiting sense.

Having now described my invention and in what manner the same may be used, what I' claim as new` and desire to protect by Letters Patent is:

1. An air compressor comprising a casing'substantially elliptical in cross section, inlet and out` let ports atopposite ends of -said ellipse, a rotor journaled in said casing. on an axis substantially concentric with one side of the ellipse between said ports,A a pluralityf of vanes movably mounted inward-ly and outwardly' of the rotor to have tangential contactA withY the inner walls of the casing, said vanes, rotor and casing together forming a pluralityof fluid chambers of constant capacity during travel between suction rand discharge sides of the compressor, means for moving said chambers from the suction to the dis` charge sides of the' compressor, atank for receiving the air pumped by said compressor, and means foraintroducing air from'said tank into said fluid chambers during travel thereofV between suction and discharge sides of the compressor in an amount suiicient to equalize the pressure betweensaid fluid chambers and said tank. y

2. An air compressor comprising a casing, a

rotor journaled in said casing on an axis sub`Y stantially-concentric with one wall ofsaid casing, inlet and outlet ports inV opposite wall portions of said casing, a plurality of vanes movably mounted inwardly and outwardly of the rotor to have tangential contact with the inner walls ofY thev casing, said vanes, rotor and casing together forming a plurality of fluid chambers of constant capacity traveling from the suction to the discharge sides of the compressor as the rotor revolves in the casing, and means for'introducingY air under discharge pressure into a plurality of .said fluid chambers in substantially all positions-of said chambers during travel thereof between suction and discharge sides of the com pressorto compress the original air in said chambersy gradually.

3; Anair compressor comprising a casing, inlet a*nd.outlet ports inopposite wall portions of said casing, arotor journaled in said casing, a

plurality of Yvanes mounted in said rotor, saidA ases-,.3172

vanes, rotor vand casing; together Yforming al plu`` rality of uid chambers traveling between suction and discharge sides of thev compressor, as

the rotork revolves in the/casing, a tank having. av

large volume relative to said chambers for receiving air discharged from said'fluid chambers, and' means for'introducing air from said tank into said fluid chambers during travel thereof between suction vand dischargesides of the compressor for in opposite portions of said casing, a plurality" of vanes mounted in said rotor, said'vanes, rotor and casing together forming a plurality of fluid chambersl between thev suction and discharge sides of said pump', a tank for receiving air discharged from said pump and constituting a source' of supply of sealing liquid for saidsaid compres`- sor, -means forf expanding 'air under pressurefrom said tank into said fluid chambers in sub'- stantially all positions of said chambers' between the suction and discharge ports in a suficientV r, volume to equalize theipressures in said tank and said Huid Vchambers during the time elapsed whilel each chamber is passing from suctiont'o discharge sides of said pump, a pipe line from saidv tank for conducting said liquid to one side of said pump casing, a second pipe line returning from the opposite side of said pump to said tank,

pump meansv for circulating said. liquid from vsaidV tank'through and around said rotor and through `said pipe lines, and a pressure regulating yvalvein r said second pipe line to control thepressure of said liquid in said casing whereby said liquid acts as a sealing means for said fluid chambers.

5. An air compressor comprising' a casing, in` let and outlet ports in opposite wall portions of said casing, a rotor journaled in said casing, a

plurality of vanes mounted inY said rotor, said' vanes, rotor and casing together forming'a plurality of fluid chambers, means for movingfsaidx chambers from the suction .to the discharge sides,"

of the compressor, a tank for receiving the air discharged from said fluid chambers and constituting'a source of supply of' sealing and cooling water for said compressor, a4 water. pump carried by said rotor capable of developing a. water pressure in excess of the air pressure in said air compressor and tank for circulating said water from said tank through said rotor and between said rotor and said casing'and'back to said tank, and' adjustable pressure` regulator means for'maintaining the pressure of said water Whiler in said casing above the pressure in said tank by a predetermined diferential. Y

6. An air compressor comprising a casing, inlet and outlet ports in opposite Wall portions of said casing, a rotor journaled in` said casing, a plurality of vanes mounted in said rotor, said vanes, rotor and casing together forming a plurality of fluid chambers, means for moving said chambers from the suction to the discharge sides of the compressor at constant volume, a tank for receiving the air discharged from said fluid chambers, a pipe line connecting ysaid tank and said casing forreturning air under discharge :pressure toA said casing, and nozzle means in said pipe to discharge said air into said chambers in substantially all positions of said chambers between. suction and `discharge sides of the compressor to establish discharge pressure in said chambers. l

'7. AnL-air compressor comprising a casing'having inlet and outlet parts, a rotor tourna-led inf.

. 9 said casing, a plurality of vanes movably mounted inwardly and outwardly of the rotor to have tangential contact with the inner Walls of the casing, each said vane being inclined in a forward direction in relation to the direction of rotation or" said rotor, said vanes tending to remain in retracted position within said rotor at normal operating speed due to the inertia of each vane, a passage extending through said rotor at the inner end of each said vane, means for admitting water under pressure through said passages for moving said vanes outwardly of said rotor and into engagement with the casing wall, pump means aiXed to said rotor for circulating said water through said passages and adjustable pressure regulator means for maintaining the pressure of said water from said pump at a predetermined pressure differential above the pressure of the air discharged from said compressor.

8. An air compressor comprising a casing, inlet and outlet ports disposed in opposite wall portions of said casing, a rotor journaled in said casing, a plurality of vanes movably mounted inwardly and outwardly of the rotor to have tangential contact with the inner walls of the casing, each said vane being inclined in a forward direction in relation to the direction of rotation of said rotor whereby said vanes tend to be held in retracted position in said rotor at normal operating speed due to the inertia of each said vane, a passage extending through said rotor at the inner end of each said vane, means for admitting water under pressure into said passages behind the inner end of each vane to cause said vanes to move outwardly of said rotor and into engagement with the casing Wall, conduit means connecting said passages and said inlet port whereby operation of said compressor may function to withdraw the water from said passages for permitting said vanesto move into retracted position in said rotor, and valve means in said conduit for controlling the Iiow of water therethrough.

9. An air compressor comprising a casing, inlet and outlet ports disposed in opposite wall portions of said casing, a rotor journaled in said casing, a plurality of vanes movably mounted inwardly and outwardly of the rotor to have tangential contact with the inner walls of the casing each said vane being inclined in a forward direction in relation to the direction of rotation of said rotor whereby said vanes tend to remain in a retracted position in said rotor at normal operating speed due to the inertia of each said vane, a passage extending through said rotor at the inner end of each said vane, means for admitting water under pressure behind the inner end of each said vane to cause said vanes to move outwardly of said rotor and into engagement with the casing wall, and means for withdrawing the water from said passages for permitting said vanes to move into retracted position in said rotor.

.10. An air compressor comprising a casing, inlet and outlet ports in opposite wall portions of said casing, a rotor journaled in said casing, a plurality of vanes movably mounted inwardly and outwardly of the rotor to have tangential contact with the inner walls of the casing, said vanes, rotor and casing together forming a plurality of fluid chambers movable between suction and discharge sides of the compressor, each said vane being inclined in a rforward direction 7 sure in the closed chamber nearest the discharge 10 ,Y in relation to the direction of rotation of said rotor whereby said vanes tend to remain in retracted position in said rotor at normal operating speed due to the inertia of said vanes, a tank for receiving air discharged from said fluid chambers and constituting a source of supply of water for said compressor, a passage extending through said rotor at the inner end of each said vane, con; duit means connecting said passages and said tank for conducting water from said tank to said passages for moving said vanes outwardly of said rotor and into engagement with the casing wall.

ll. An air compressor comprising a casing, inlet and outlet ports in opposite wall portions of said casing, a ro'tor journaled in said casing, a plurality of vanes movably mounted inwardly and outwardly of the rotor to have tangential contact with the inner walls of the casing, said vanes, rotor and casing together forming a plurality of fluid chambers movable between suction and discharge sides of the compressor, each said vane being inclined in a forward direction in relation to the direction of rotation of said rotor whereby said vanes tend to remain in retracted position in said rotor at normal operating speed due to the inertia of said vanes, a tank for receiving air discharged from said fluid chambers and constituting a source of supply of water for said compressor, a passage extending through said rotor at the inner end of each said vane, conduit means connecting said passages and said tank, pump means for circulating water from said tank through said passages and conduit means, a return pipe line connecting said passages and said tank, and a pressure regulating valve in said return pipe line, said pump means and said pressure regulating valve coacting to increase the pressure of water in said passages to a predetermined pressure differential in excess of the pressure existing in said tank.

l2. An air compressor comprising a casing, inlet and outlet ports in opposite wall portions of said casing, a rotor journaled in said casing, a plurality of vanes mounted in said rotor, said vanes, rotor and casing together forming a plurality of fluid chambers between the suction and discharge sides of the compressor, a tank for receiving air discharged from said fluid chambers and constituting a source of supply of lubricating and sealing water for said compressor, pump means affixed to one side of said rotor for circulating water through and around said rotor, conduit means connecting said tank and said pump means, a return pipe line connecting said casing and said tank for returning said circulating water from said pump to said tank, and a pressure regulating valve in said return pipe line, said pump means and said pressure regulating valve coacting to maintain the water in said casing at a predetermined pressure differential above the air discharge pressure of the compressor.

' 13. An air compressor comprising a rotory vane type pump having vanes forming constant volume chambers movable between suction and discharge ports in the compressor, a tank connected with said discharge port to receive compressed air from said compressor, and a separate pipe from said tank to said pump `for expanding air from said tank into said chambers in substantially all positions of said chambers as they move from said suction to said discharge ports and in a volume suflicient to cause the air pres- Maiselr port to equal the tank breesure .whereby al1 the compression in said pump is produced by the expanson of air circulated from said tank.

DANIEL F. MCGILL.

Number Number Name Y Dat Kenney,.et a1. Sept. 28, 1937 Steenstrup Dea-14, 193,7 Nichols Noy. 8, 1938 Patterson Feb. 28, 1939 Taglio Feb. 13, 1940 Davidson June 17, 19.41 Beckman July 2 0, h1943 Kendrick Nov. 30, 1943 FOREIGN PATENTS Country Date Great Britain Aug. 1:7, 1912 Great Britain May 31, 1928 Great Britain Mar. 22, V1939 Germany Nov. 14, 1932` 

